Alternator charging at idle

[Lump]

I recently exchanged the lucas alt on my chev v8 enginge with a GM alternator(this was supposed to be 80 amps but apparently it is only 65 amps)

I was hoping to improve charging at idle as with the lucas alt it would drop down to about 12volts at idles and below that if the lights or electric fan came on.

The GM alternator behaved identically at first, however I replaced the battery which was nearing the end of its life at the situation improved a little. Basically i get good voltage readings over about 1000 rpm (14v sort of territory) however when the car is at idle in gear (600 rpm) I get about 12.4 volts but with electrical load (i.e. headlights and twin radiator fans on it drops down to 11.9volts) - with the car not running and the same electrical load I still get 11.9v.

I know these readings are probably fine but I'd be happier if the voltage at idle and under load was at least 12.4 volts could this be improved by fitting a larger alternator say 105 amps or would I still have the same charging problems at idle?

[UTERUS]

I know nothing about GM alternators but has it got internal or external regulator? Is there any adjustment on it?

Higher current alt won't help as far as i know.

You aren't often idling in gear are you? Usually it's followed by acceleration for some high voltage charging action.

Edit: The voltage of the alt is based on the speed, you can't really force a magnetic field to output a certain voltage when it is spinning below it's designed working rpm.

[Unclejake]

Lump, I think the behaviour you are seeing is pretty normal.

To achieve what you want you will need to change the gearing of the alternator. Find a smaller alternator pulley to fit onto your existing alternator and you will have more charge at idle.

[Bling]

Increase your idle speed? Haven't seen an idle that low

[kyteler]

Increase your idle speed? Haven't seen an idle that low

Most older cars with manual transmission run idle from 550-650rpm, Automatic from 750-850rpm

[Vai-Man]

Yuh smaller pully on the alt would work but might stress the alt at high revs?

In the fiat the gauge pretty much reads the same 12 at idle but 14 when on the move, Your lights etc dont go dim or the stero cuts out or anything at idle do they?

[Unclejake]

Yuh smaller pully on the alt would work but might stress the alt at high revs?

great point but that shouldn't be a problem in a Chev V8 in a road car as they don't rev very high

[dave123456789]

I have the same problem in my prince gloria although when I am driving it goes up to about 12.5 on the gauge and sits under 12 if I drive with lights on, cant use my car at night

[kyteler]

I have the same problem in my prince gloria although when I am driving it goes up to about 12.5 on the gauge and sits under 12 if I drive with lights on, cant use my car at night

Yours is likely just the regulator, if it's the original engine, it's likely an external regulator, you can get replacements from APPCO, BNT, etc. So do that, but make sure it's the right one for the car. If you're not fussed about keeping it original, you could convert to a modern, internally regulated alternator. It's just a matter of adding a few extra wires to the plug that would have gone to the external regulator and then getting a suitable preferably higher amperage internally regulated alternator with the right mount positions to bolt in place.

What generation of Prince Gloria do you have?

[David]

Are you testing the voltage at the battery or the alternator?

Has the motor got a good earth?

Does the starter struggle?

Are you using the factory Jag wiring or new?

First test would be voltage drop. (Bad connections)

With the lights and a bit of electrical load, set your meter to DC volts and try putting the one prob of your meter on the engine block and the other prob on the NEG battery terminal. ( Motor going, be carefull not to get leads wound up in the fan). This is testing for voltage drop. 0.0V is best, say anything over 0.5V you should investigate cleaning earthing contact areas. No joy? look at the positive side of the system for bad connections.

If you have a meter with a DATA MAX hold is best, you can try hitting the starter and see how bad any voltage drop is also.

Reduction starter? (often fitted for better steering clearance with the SB in a XJ6)

If you have a SB chev with a reduction starter you may not even notice a smaller voltage drop from bad connections. I've seen these drop down to 9V when starting, and still crank well.

Just recommend these tests, as cleaning turminations is the cheapest repair. (before spending money)

**Off topic**

Did you have to change your front springs in the XJ6 to get it back to the right ride hight with the V8?

[Lump]

Are you testing the voltage at the battery or the alternator?

Has the motor got a good earth?

Does the starter struggle?

Are you using the factory Jag wiring or new?

First test would be voltage drop. (Bad connections)

With the lights and a bit of electrical load, set your meter to DC volts and try putting the one prob of your meter on the engine block and the other prob on the NEG battery terminal. ( Motor going, be carefull not to get leads wound up in the fan). This is testing for voltage drop. 0.0V is best, say anything over 0.5V you should investigate cleaning earthing contact areas. No joy? look at the positive side of the system for bad connections.

If you have a meter with a DATA MAX hold is best, you can try hitting the starter and see how bad any voltage drop is also.

Reduction starter? (often fitted for better steering clearance with the SB in a XJ6)

If you have a SB chev with a reduction starter you may not even notice a smaller voltage drop from bad connections. I've seen these drop down to 9V when starting, and still crank well.

Just recommend these tests, as cleaning turminations is the cheapest repair. (before spending money)

**Off topic**

Did you have to change your front springs in the XJ6 to get it back to the right ride hight with the V8?

I'm away for a few days a the moment so I'll do the tests you suggest when I get back and post the results here.

The alternator wiring is part Jag part custom, the main power feed from the alternator has been extended for the conversion (joints appear well done) the wires core is 4mm at the narrowest points. I've added a voltage sense wire for the GM alt and I'm using the idiot light wiring fitted from the factory.

I have smaller than usual starter motor (branded Bosche - this was fitted to the car when I brought it and yes it is a tight fit in this area)I've had problems with a sluggish starter in the past but it is fine now that the timing has been set correctly.

My car was converted when I brought it but to get the correct height at the front of the car I'm told you need to remove some of the spring spacers (there are 6 fitted each side - 3 top -3 bottom) leaving one spring spacer on the top and bottom of each spring will give you the correct ride height with the lighter chev engine.

[David]

http://home.clear.net.nz/pages/phil.bra ... wiring.htm

and go down to: Wire Current Ratings ( look about right )

Just as a guess with the XJ6 there will be about 1.5 Metres of wire between the alternator Positive and the battery, 4mm wire is a bit small, but would be normal for Jag.

A quick look at the table and take a stab at 30Amps for a bit of charging , fans , lights.

1.5 metres x 30 Amps x 10mV drop (4mm wire) = 450mV (.45V) drop

Taking into consideration, voltage drop in the negitive side and some loss for every connection, then 0.8V to a 1.0V voltage drop wouldn't be hard. Give it some low idle speed and it seems about right.

If the tests with your meter show a loss in voltage and you fell the earthing is no good, try testing with a tempory jumper lead from the battery negative to the alternator body and see if this helps before buying earth straps and larger wire.

You may look at the table and say 16mm wire lines up with 68 Amps. It's very rear you will ever continuisly draw this amount of current for a long time. Half way between size like 6mm or 10mm would do.

[forced]

I was hoping to improve charging at idle as with the lucas alt it would drop down to about 12volts at idles and below that if the lights or electric fan came on.

?

As already mentioned, although an alternator puts out more than a "generator" at idle, it still doesn't put out a great deal. They need to be revved to put out the max rated output. What you're seeing is pretty much normal.

BTW is that the XJ6 that used to live in Wainui recently?

Steve

[Lump]

I've tested the voltage drop and it doesn"t get higher than 0.03 volts under load so I guess its pretty good.

I couldn't find any voltage drop when the starter activated although reading the voltage at the battery it was at 10.8V at its lowest reading when the starter was on - again not bad.

In conclusion it would seem that there's nothing really wrong with my charging system and I've been a dumb/fussy cunt thinking more volts are best.

Thanks for your help guys

PS I've had the jag for a few years so its not the one from Wainui